The present invention relates to a doctor blade mounting structure for mounting a doctor blade to a development unit of an imaging apparatus using of electrophotography.
In a known imaging apparatus such as an electrophotographic copy machine, laser beam printer and the like using electrophotography, an electrostatic latent image is formed by exposing the surface of a photoconductive drum formed of a photoconductive material, toner is adhered onto the latent image and developed, and then the toner is transferred onto a recording paper and fixed by a fixing unit.
Although various systems are contemplated as development methods in electrophotography, a system referred to as a magnetic brush method is widely used, wherein charged toner is supplied to an electrostatic latent image by a magnetic material carrier (magnetic brush) arranged in a chain shape by a magnet.
Although the magnetic brush method employs a two-component developer composed of non-magnetic toner mixed with a magnetic material carrier at a preset ratio, recently a so-called 1.5 component development is employed, wherein one-component charged type magnetic toner is used and a magnetic material carrier is predeposited onto a development roller.
A development unit to which the magnetic brush method is applied includes a development roller formed by rotatably installing a sleeve of a non-magnetic material around the periphery of a magnetic roller with toner sequentially supplied to a development area by rotating the sleeve of the development roller.
To develop a good image, the magnetic brush must be disposed on a uniform level with pinpoint accuracy. Thus, a flat-plate-shaped doctor blade is provided in confrontation with the outside periphery of the development roller (the outside periphery of the sleeve) and a predetermined gap (doctor gap) is set between the extreme end of the doctor blade and the outside periphery of the development roller to thereby regulate the height of the magnetic brush.
The doctor blade is adjusted in such a manner that a gage having a thickness similar to a doctor gap to be set is held between the outside periphery of the development roller and the extreme end of the doctor blade to thereby evenly press and fix the doctor blade.
Nevertheless, a problem arises in that it is very difficult to fix the flat-plate-shaped doctor blade extending over the entire longitudinal length of the development roller with respect to the development roller with a doctor gap evenly adjusted over the entire longitudinal extent of the development roller. More specifically, since the flat-plate-shaped slender doctor blade is originally very deformable by itself, it is very difficult to obtain a machining accuracy such as a straight line accuracy and suppress the occurrence of a twisted portion and the like, thus the cross section of the doctor blade must be increased by making the blade thicker to prevent the deformation thereof by providing it with rigidity. However, but the increase in the cross section of the doctor blade increases the size of the development unit. Accordingly, the size of an imaging apparatus increase using the development unit as a whole. Thus, the increase of the cross section of the doctor blade is not preferable. As a result, a deformable doctor blade must be abutted against a gage horizontally abutted against or fixed to the outside periphery of the development roller over the entire length thereof by applying an even pressing force and fixed thereto by a plurality of clamping screws. Thus, an adjusting job is time consuming and the doctor blade is difficult to be set and adjusted with pin-point accuracy.